It's far cheaper for a company to buy machinery to weld together aluminum, and steel frames without lugs, than it is to hire trained professional artisans to butt braze lugged frames. Period.
Believe it or not, back in the forties and fifties it was possible to buy a custom made hand built but plain Jane frames for as low as $35
Lugged steel frames, especially when the lugs are filed into fancy designs are beautiful and ride very nicely indeed!